1. Technical Field
The present invention relates to a matrix printhead of a wire matrix printer, and more particularly to a method for manufacturing a print wire for use in a 24-pin dot printhead.
2. Background Art
Wire matrix printers are well known in the contempory art. Conventional matrix printers typically use a plurality of thin elongated print wires arranged in matrix fashion for making impact through a ribbon to impress the ink onto a printable medium whereby the print wires are selectively energized to form characters, numerals or other symbols. Each print wire typical has an impact receiving end and a printing end which contacts the ribbon so that a minute dot is imprinted on the printable medium. The result is a pattern of dots formed on the paper in a configuration corresponding to the desired character.
In the past, the impact receiving end of each print wire is typically designed to consist of a spiral or pig-tail like meets of wire covered in plastic; but this type of design was extremely weak at the joint where the spiral loop meets the wire stem and was consequently susceptible to high stress concentration, fatigue and eventual failure in the matrix printhead application. Improvements on the plastic covering the impact receiving end of the print wire is shown in U.S. Pat. No. 4,143,979 issued to Boyd for Printhead Needle Cap, while other designs simply sought to weld or braze a needle cap onto the end of the solid print wire. A needle cap could be replaced by a cylindrical collar as shown in U.S. Pat. No. 4,569,604 issued to Adachi et al. for Printing Head Apparatus And Manufacturing Method. Different designs on the impact receiving end of the print wire are disclosed in U.S. Pat. No. 3,718,968 issued to Sims et al. for Method For Connecting A Wire To A Component and U.S. Pat. No. 4,256,948 issued to Wolf et al. for Integral Bead Stylus Wire And Method Of Making Same where the impact receiving end of each print wire is melted by laser or plasma welding into a solid sphere-like head. The main problem with these designs is that they require costly manufacturing steps. The same is also true with a more sophisticated design disclosed in U.S. Pat. No. 4,867,583 issued to Caulier et al. for Dot Matrix Printer/Module Using Print Wires Having Different Length But Equal Mass where the print wire is a low mass hollow steel tube and the needle cap is a high wear resistant preform head designed to insert into the print wire for strong attachment.